1. Field of the Invention
The present invention relates to a mobile communication system, a core network apparatus, and an MBMS data transmission method used for them, and more particularly, to a method for transmitting Multimedia Broadcast Multicast Service (MBMS) data in an Evolved Universal Terrestrial Radio Access Network (E-UTRAN).
2. Description of the Related Art
In Release 7 and onwards of the Third Generation Partnership Project (3GPP) standardization, a next-generation network is now under consideration as Long Term Evolution (LTE)/System Architecture Evolution (SAE).
The 3GPP Release 6 has defined a feature called MBMS which is intended for distribution of video, picture, and/or music data (see “Introduction of the Multimedia Broadcast Multicast Service (MBMS) in the Radio Access Network (RAN); Stage 2 (Release 6)” (3GPP TS25.346 V6.5.0 (2005-06)), for example), and the way of realizing the feature in the system based on Release 7 and onwards is being discussed.
However, in the E-UTRAN system configuration which has been incorporated as a requirement from Release 7 and onwards, a Radio Network Controller (RNC) is integrated with a NodeB (a radio base station) to become an eNB (E-UTRAN NodeB), and an interface with a core network apparatus (User Plane Entity (UPE)/Mobility Management Entity (MME)) is an Internet Protocol (IP) network. For these reasons, it has not been specifically defined how to absorb delay or fluctuation on a transmission link, a point at which MBMS data from a Broadcast Multicast-Service Centre (BM-SC) is copied and transmitted on a cell basis, and/or how to synchronize data transmitted by eNBs when User Equipment (UE) moves across cells of different eNBs.
An MBMS service in a network configuration of a related art is conceptually illustrated in FIG. 7. As shown in FIG. 7, synchronization processing is performed between an RNC 7 and NodeBs (#1, #2) 6-1, 6-2. From this synchronization, the RNC 7 recognizes delay on transmission links to the NodeBs (#1, #2) 6-1 and 6-2, and performs processing for copying MBMS data which is received from the BM-SC 5 via a GGSN (Gateway GPRS (General Packet Radio Service) Support Node) 9 and an SGSN (Serving GPRS Support Node) 8 on a cell basis and transmitting the MBMS data to UEs (#1, #2) 1-1 and 1-2 via the NodeBs (#1, #2) 6-1 and 6-2.
Techniques for multicast transmission in a network configuration of a related art include the one described in Japanese Patent Laid-Open No. 2004-229117.
While E-UTRAN is currently under consideration, when an MBMS service is to be realized in the current system, the NodeB and the RNC is synchronized with each other, and the RNC performs data copying processing in consideration of the cells of the NodeB.
In the E-UTRAN, on the other hand, the functions of the RNC and those of the NodeB are integrated and defined as an eNB. Consequently, there are a problem that a point for copying MBMS data when an MBMS service is realized is not specifically defined, and a problem that the way of synchronization is not defined though it is necessary to synchronize MBMS data transmitted by eNBs into Air (or a wireless space) in order to realize a seamless service when UE moves across cells of the eNBs. These problems cannot be solved even with the technique described in Japanese Patent Laid-Open No. 2004-229117.